Fullauto head before and after comparisons (2014)

Bernhard said:

You were NOT buying a hand built race fettered motorcycle, so anybody who had a shed with the right knowledge could build a better, faster engine than was the norm.
For instance, anybody could just polish the cylinder head ports that would gain a bike length from a standing start

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I wasn't suggesting that BSA should have sent all the bikes out with blueprinted engines. If they had just bothered to make the bloody things to their own drawings they might still be in business. As was pointed out earlier, the Lightning heads made more power when made to the drawings. Trident heads were the same. Some of the castings were very restricted on the centre port, so much so that even a half wit could see they were wrong, but they still sent them out to paying customers.

My 850 Commando does not have any intrusive vibration at any revs. It wasn't always like this. When I fitted my CNW/Jim Comstock head steady, the side to side movement was eliminated, so with a bit of deduction, I backed the rear isolastics off somewhat more than recommended and was rewarded with smooth running at all revs. Conventional Norton lore would have it that then I would get a nasty hinge in the frame. Well, you would with the standard Norton "headsteady", but not the far better engineered Jim Comstock unit. My Commando remains the best handling Commando I have ever ridden. And ultra smooth to boot.

Matchless said:

I wasn't suggesting that BSA should have sent all the bikes out with blueprinted engines. If they had just bothered to make the bloody things to their own drawings they might still be in business. As was pointed out earlier, the Lightning heads made more power when made to the drawings. Trident heads were the same. Some of the castings were very restricted on the centre port, so much so that even a half wit could see they were wrong, but they still sent them out to paying customers.

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On the production line there will be a mixture of skills, some of them will be skilled, others semi skilled, the rest unskilled and not bothered at all. The management should have had inspection system set up to prevent any components being fitted to the finished bike.
But margins are tight, and they cannot afford to scrap a whole batch unless they are completely unserviceable. I've worked in factory's and some people produce crap day in day out that I can't , for the life of me, understand why the company employs them.

It wasn't just BSA. John Healy mentions the need to rework valves on new late 60s early 70s Triumph 650/750.
Never mind gastight, with the head off , daylight was visible between the valve and valve seat. Apparently the guides and seats were seriously out of alignment. Of course this resulted in lots of compression leaking away along with power.

Glen

Bernhard said:

You were NOT buying a hand built race fettered motorcycle, so anybody who had a shed with the right knowledge could build a better, faster engine than was the norm.
For instance, anybody could just polish the cylinder head ports that would gain a bike length from a standing start

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That's possibly quite true. I actually tried this some time ago, cleaned up a stock head and smoothed all the bumps and blended the seats, I thought I was kicking butt. It's never been used and I tested it, it's gone from around 109cfm to 114cfm. It would go marginally better than stock.

The one I'm messing with now has a stock valve and at stock lift, it's saying it's 164.4cfm, it's for a 34mm carb. The reading might be wrong but it's miles different without being much bigger. The stock cleaned up head with the test vacuum wound up by 4", possibly like having more engine displacement and hotter cam causing more suck, still only makes 135cfm, it's like it's blocked. The little port is really finicky though, it cannot have ridges and stuff. I got a tiny grinder to get rid of the ridge between the alloy port and steel or iron insert for the valve seat. The other side is a bit behind but I should be able to get that.

As far as I've ever seen later brit bikes were built of mixed quality parts bolted up and tossed out the door. You can get a
good sample but you are the lucky one. If you were talented and well tooled you could fettle the bike to a decent state.
Vast majority of buyers were not able to do this. Honda and the other jap manufacturers churned out vast numbers of bikes
that were almost all of high quality. They had the owners, investment, management, engineering and workforce who were all
on the same path. Each year brought improvement and new designs. None of this really happened in the UK or in the USA.
We have a better chance at sorting a bike of that time out now than most of us did back then.

Onder said:

As far as I've ever seen later brit bikes were built of mixed quality parts bolted up and tossed out the door. You can get a
good sample but you are the lucky one. If you were talented and well tooled you could fettle the bike to a decent state.
Vast majority of buyers were not able to do this. Honda and the other jap manufacturers churned out vast numbers of bikes
that were almost all of high quality. They had the owners, investment, management, engineering and workforce who were all
on the same path. Each year brought improvement and new designs. None of this really happened in the UK or in the USA.
We have a better chance at sorting a bike of that time out now than most of us did back then.

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Thought i was in the 961 section for a moment, plus ca change...

This is just a bit of an update on the BSA 734. this has changed from a pair of 38mm carbs to 34mm. It's possible to retain flow as the restriction in the head isn't the port runner size. Many talk about optimizing port speed, so this is doing this by reverse porting. Arriving at an adequate cfm figure then closing down the port runner until that size is reduced closer to minimum while still having the flow. So this flow is obtained by shape, not size and the results confirm the value. It changes a bit in being more particular to shape but raises gas speed which has a very nice affect and the engine produces far more drive at lower rpm. It's more tractable sweet and punchy. Much like having a bigger engine. It's very alive.

Matt Spencer said:


Before I fitted mine , I had to pass all the Hondas on the corners , could only hold them on the straights , and the cop bikes couldn't be shaken off .
Now itll even get the kawasakis on the straights , and the last time he tried it the cop ran outve brakes into the bend and hasn't been seen again .

:wink: :lol: :lol: :? :lol:

Er . . .

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Not sure about this , but at the time I thought a ' HACK ' had occurred . Same ' Vibe ' subjugation seeing this recalls it .
Similar but not as evasive to comprehend as my artistry !

Though otherwise a Sore head & a lack of patiance with something mightve explained it .
Same sore head as when I first saw it .
Explain That & I will know who is behind it . thanks .

Bernhard said:

You were NOT buying a hand built race fettered motorcycle, so anybody who had a shed with the right knowledge could build a better, faster engine than was the norm.
For instance, anybody could just polish the cylinder head ports that would gain a bike length from a standing start

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Polishing intake ports is counterproductive. A slightly rough intake port surface helps prevent fuel drop out.

A polished exhaust port helps prevent carbon buildup.

You can get more air through with polished but it doesn't make up for shape and smoothness, being without jumps and bumps. If it looks like it's been finished with a brick I think it's counter productive, I remember seeing that in a Ducati shop when I was young. Good quality performance jobs look smooth.
The advantage with the BSA head is although like others the port cannot go very high near the guide, it can go wide. The std 68-701 head is only 17-18mm wide at the guide, BSA used a special head on the Mk4 Spitfire in 1968, it had 9-1 pistons not 10-10.5-1 like its predecessors but made more power. Flow was better in the region of 109cfm to 139cfm, the big difference was opening up that restriction and turning the charge with a deeper bowl. They deepened it by 2mm and widened it at the guide from 17-18mm to 32mm, it was that simple.

The A65 can go quite wide, so comparing that with a ported 34mm port head using a 42mm valve, it's 40.5mm deep in the bowl and 39mm wide at the guide, if the air is going round the guide you just make space, without that space it doesn't venturi to any good effect, it blocks, the floor is lifted to turn it and flow jumps to 165cfm or 179cfm with a bell because it becomes very particular about having a smooth entry when speed gets over 400fps, otherwise it rips off the sharp edge of the port and blocks it with turbulence I expect, speed is down on the edges and up in the centre.
This is looking down a 34mm oval port using a 44.5mm valve. The dark areas are fill. It shows how it's wide at the guide so the air can simply go around, take the valve out it flows less air. This one flows over 190cfm and is like the one on the 734. If you are wondering why they are oval it's because of limiting height in the head and both top and bottom need smooth curves, the air is forced around the top, the wall it runs into turns it. if it goes down before the guide then back up the air leaves the wall. On the bottom it just lifts it a bit before curving down onto the valve.

mark parker said:

...., the floor is lifted to turn it and flow jumps to 165cfm or 179cfm with a bell because it becomes very particular about having a smooth entry when speed gets over 400fps, otherwise it rips off the sharp edge of the port and blocks it with turbulence ,,,

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Describe what you mean by "bell"

mark parker said:

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A radiused entry.